Tens Of Millikelvin Research Articles

Cryogenic phonon-detector model with solid argon for detecting dark matter* *This work is supported by the National Key Research and Development Program of China (2017YFA0402203) and the National Natural Science Foundation of China (12075161)

Over the past few years, phonon detectors have emerged as a prevailing technology for detecting low-mass dark matter due to their low thresholds and high resolution. These detectors, which employ either dual-phase detectors combining phonon-light or phonon-electron interactions, have significantly advanced direct dark matter detection efforts. Argon, as a low-background and high-reserve detection medium, has also played a crucial role in this field. Both liquid-argon single-phase detectors and gas-liquid two-phase time projection chambers (TPCs) have contributed substantially to the direct detection of high-mass dark matter. By integrating these distinct detector types, the upper limits of the corresponding mass cross-section in dark matter detection can be lowered. We propose a phonon detector utilizing solid argon as the absorber, which combines the advantages of both aforementioned detector types. However, due to the requirement for an ultra-low temperature environment in the tens of millikelvin (mK) range, experimental investigations of solid argon phonon detector performance are currently constrained by technical limitations. Therefore, the performance analysis of the solid argon phonon detector presented in this study is only based on sapphire phonon detectors. Although there may be discrepancies between this approximation and the actual performance, the intrinsic characteristics of phonon detectors permit a qualitative evaluation of the solid argon phonon detector's potential capabilities.

Quantifying the effects of dissipation and temperature on dynamics of a superconducting qubit-cavity system

The superconducting circuits involving Josephson junction offer macroscopic quantum two-level system (qubit) which are coupled to cavity resonators and are operated via microwave signals. In this work, we study the dynamics of superconducting qubits coupled to a cavity with including dissipation in a subKelvin temperature domain. In the first step, a classical finite element method is used to simulate the cavities and basic circuit elements to model Josephson junctions. Then, the quantization of the circuit is done to obtain the full Hamiltonian of the system using energy participation ratios of the junctions. Once the parameters of Hamiltonian are obtained, the dynamics is studied via the Lindblad equation for an open quantum system using a realistic set of dissipative parameters and include temperature effects. Finally, we get frequency spectra and/or dynamics of the system with time which have quantum imprints. Such devices work at tens of milliKelvins and we search for a set of parameters which could enable to observe quantum behaviour at temperatures as high as 1 K.

Cryo-CMOS Electronics For Quantum Computing: Bringing Classical Electronics Closer To Qubits In Space And Temperature

The core of a quantum computer is a quantum processor, which is composed of quantum bits (qubits). Qubits can be implemented in many flavors, but they are fragile, and their state has a tendency to decay in time. To be usable for computation, qubits must be corrected in real time by a classical controller. The controller must also see that desired computations are executed. Today, the control of qubits is performed at room temperature (RT) by racks of instruments, while the qubits operate at several tens of milli-Kelvin. To ensure compactness and, eventually, scalability, we have proposed and implemented CMOS circuits designed to operate at a few degrees Kelvin. This makes complex thermalization circuits unnecessary, potentially enabling superconductive interconnects, which would enable virtually zero resistance and low thermal conductivity. Cryogenic CMOS, or cryo-CMOS, technology was chosen to achieve classical control due to its scalable nature and overall miniaturization opportunities. Cryo-CMOS circuits and systems need to be carefully designed to ensure strict power budgets, while achieving quite advanced specifications in terms of noise and bandwidth. We review the requirements of a classical controller and cryo-CMOS circuits and systems developed for spin qubits in our lab. Results and perspectives are presented with a discussion about a road map for the future.

Absence of long-range order in an XY pyrochlore antiferromagnet Er2AlSbO7

Rare-earth pyrochlores are known to exhibit exotic magnetic phenomena. We report a study of crystal growth and characterizations of a new rare-earth compound Er$_2$AlSbO$_7$, in which Al$^{3+}$ and Sb$^{5+}$ ions share the same positions with a random distribution. The magnetism are studied by magnetic susceptibility, specific heat and thermal conductivity measurements at low temperatures down to several tens of milli-kelvin. Different from the other reported Er-based pyrochlores exhibiting distinct magnetically ordered states, a spin-freezing transition is detected in Er$_2$AlSbO$_7$ below 0.37 K, which is primarily ascribed to the inherent structural disorder. A cluster spin-glass state is proposed in view of the frequency dependence of the peak position in the ac susceptibility. In addition, the temperature and field dependence of thermal conductivity indicates rather strong spin fluctuations which is probably due to the phase competition.

Radiative Cooling of a Superconducting Resonator.

Cooling microwave resonators to near the quantum ground state, crucial for their operation in the quantum regime, is typically achieved by direct device refrigeration to a few tens of millikelvin. However, in quantum experiments that require high operation power such as microwave-to-optics quantum transduction, it is desirable to operate at higher temperatures with non-negligible environmental thermal excitations, where larger cooling power is available. In this Letter, we present a radiative cooling protocol to prepare a superconducting microwave mode near its quantum ground state in spite of warm environment temperatures for the resonator. In this proof-of-concept experiment, the mode occupancy of a 10GHz superconducting resonator thermally anchored at 1.02K is reduced to 0.44±0.05 from 1.56 by radiatively coupling to a 70mK cold load. This radiative cooling scheme allows high-operation-power microwave experiments to work in the quantum regime, and opens possibilities for routing microwave quantum states to elevated temperatures.

Light Induced Electron-Phonon Scattering Mediated Resistive Switching in Nanostructured Nb Thin Film Superconductor

abstractThe elemental Nb is mainly investigated for its eminent superconducting properties. In contrary, we report of a relatively unexplored property, namely, its superior optoelectronic property in reduced dimension. We demonstrate here that nanostructured Nb thin films (NNFs), under optical illumination, behave as room temperature photo-switches and exhibit bolometric features below its superconducting critical temperature. Both photo-switch and superconducting bolometric behavior are monitored by its resistance change with light in visible and near infrared (NIR) wavelength range. Unlike the conventional photodetectors, the NNF devices switch to higher resistive states with light and the corresponding resistivity change is studied with thickness and grain size variations. At low temperature in its superconducting state, the light exposure shifts the superconducting transition towards lower temperature. The room temperature photon sensing nature of the NNF is explained by the photon assisted electron-phonon scattering mechanism while the low temperature light response is mainly related to the heat generation which essentially changes the effective temperature for the device and the device is capable of sensing a temperature difference of few tens of milli-kelvins. The observed photo-response on the transport properties of NNFs can be very important for future superconducting photon detectors, bolometers and phase slip based device applications.

A comparative study of ultra-low-temperature thermal conductivity of multiferroic orthoferrites RFeO3 (R = Gd and Dy)

Ultra-low-temperature thermal conductivity (κ) of GdFeO3 and DyFeO3 single crystals is studied down to several tens of milli-Kelvin. It is found that the κ is purely phononic and has strong magnetic-field dependence, indicating a strong spin-phonon coupling. Moreover, the low-T κ(H) with H∥c show rather different behaviors in these two materials. In particular, the κ of GdFeO3 can be strongly enhanced in several tesla field and becomes weakly field dependent in higher fields up to 14 T; whereas, the κ of DyFeO3 is continuously suppressed with increasing field and does not show any signature of recovery at 14 T. The results can be well understood by the difference in the spin anisotropy of Gd3+ and Dy3+ ions.

Influence of the Opening of a Blackbody Cavity Measured at the Ag and Cu ITS-90 Fixed Points

The International Temperature Scale of 1990 blackbody fixed points are commonly composed of a graphite crucible containing a pure metal enclosing a radiating blackbody cavity. The shape of the cavity is determined to behave as much as possible as a perfect blackbody; however, the opening from which the radiance is measured induces radiative losses. The measured temperature is therefore underestimated by a few tens of millikelvins at \(1000\,^\circ \)C, compared to that of a perfect blackbody. The difference is due, on the one hand, to the drop of emissivity caused by the opening, and on the other hand, to the temperature drop between the solid/liquid interface and the inner wall of the cavity, observed by the radiation thermometer. The temperature drop is generally estimated by modeling the emissivity and the temperature difference across the cavity wall. This approach is relevant as long as the temperature distribution along the cavity and the graphite properties are known, but in many cases, the lack of data does not allow precise determination of the corrections. The corrections for the temperature drop and emissivity drop, which both depend on the cavity opening, can be determined experimentally with a low uncertainty by measuring the temperature of a fixed point for different cavity openings. To be significant, the measurement requires a source stable within a few millikelvins. In this study, this constraint has been solved by changing the cavity opening during the phase transition of the fixed point, with a rotating wheel supporting apertures of different dimensions. Measurements have been performed at the Ag and Cu fixed points during the freezing plateaus. Experimental results are presented and compared to those obtained by modeling.

Metal Bulk Foil Resistor Characterization for BAW Application at Low Cryogenic Temperatures

We report on the development of a characterization system and calibration procedure for a bulk acoustic wave (BAW) resonator using a bulk metal foil resistor operated at temperatures as low as tens of millikelvin. The 50-Ω resistor demonstrated extremely good stability and small drift at a temperature of 50 mK, with the resistance varying by 1.5% between room temperature and 50 mK. The BAW quartz resonator exhibited a quality factor of 8×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> at 206 MHz, which is one order of magnitude higher than state-of-the-art equivalent devices at ambient temperature. Such results were obtained due to the combination of a suitable technology of resistor, and the custom design of an electronic circuit board for calibration.

Approximating the ITS-90 Temperature Scale with Industrial Platinum Resistance Thermometers

Platinum resistance thermometers (PRTs) are widely used for accurate temperature measurements in industrial process control as well as in testing and calibration laboratories. Industrial-type PRTs (IPRTs) are available with platinum wires of different purity and can attain measurement accuracy at the level of few tens of millikelvin in a broad temperature range from −196 °C to 550 °C and above. For such IPRTs, the most-used interpolation model (resistance versus temperature) is based on the Callendar–Van Dusen (CVD) equation, which is also recognized in several industrial standards including IEC 60751 and the corresponding national standards. In recent years, several studies have shown that systematic differences exist between the ITS-90 temperature (T 90) and the temperature calculated by the CVD function. When the CVD equation is used to fit experimental data, the difference can be as large as several tens of millikelvin, even near a calibration point, i.e., of the same order of magnitude as the experimental uncertainty routinely achieved in laboratory calibrations. In order to overcome the above limitations, many interpolation models were proposed. The aim of this work is to assess the use of ITS-90 defining equations in precision laboratory calibrations of IPRTs in the temperature range from −196 °C to 420 °C. Twenty IPRTs with W(100) ranging from 1.384 to 1.392 were calibrated by comparison against a standard PRT, and the experimental data were processed using several interpolation schemes based on ITS-90 deviation functions with different degrees of freedom. The overall results showed that any ITS-90-based scheme performs better than the CVD equation, suggesting that it be applied to a broad spectrum of industrial and laboratory applications.

Characterization of a fabrication process for the integration of superconducting qubits andrapid-single-flux-quantum circuits

In order to integrate superconducting qubits with rapid-single-flux-quantum (RSFQ)control circuitry, it is necessary to develop a fabrication process that simultaneouslyfulfils the requirements of both elements: low critical current density, very lowoperating temperature (tens of millikelvin) and reduced dissipation on the qubit side;high operation frequency, large stability margins, low dissipated power on theRSFQ side. For this purpose, VTT has developed a fabrication process based onNb trilayer technology, which allows the on-chip integration of superconductingqubits and RSFQ circuits even at very low temperature. Here we present thecharacterization (at 4.2 K) of the process from the point of view of the Josephsondevices and show that they are suitable to build integrated superconducting qubits.

Observations on Photo-Emission and the Process Zone of a Fatigue Crack

Abstract Cyclic loading of a solid material induces a cyclic temperature fluctuation. The thermal cycle is asynchronous with the loading cycle when the strains are elastic. This is commonly known as the thermoelastic effect. In differential thermography, a sensitive infrared camera is used to measure this temperature variation; typically of the order of a few tens of milliKelvin. Since the magnitude of the temperature variation is proportional to the dilational strain, values of the surface elastic stress can be derived. Recent advances in infrared camera technology and data processing algorithms have enabled values of effective stress intensity factor ranges and the location of fatigue cracks to be determined from temperature fluctuations around the crack tip on the specimen surface. Careful observation in the region near a crack tip reveals deviations from the asynchronous behavior of the photon signal relative to the load cycle. Phase shifts up to π/8 are commonly observed. The spatial distribution of these phase shifts exhibits characteristic features which are described and discussed. The features in this distribution appear to be associated with high elastic strain gradients, regions of plasticity and contact between the crack faces. Interpretation of the phase shift and its spatial distribution may lead to a better understanding of the mechanics of fatigue crack growth.

Rapid viscous flow of a nematic liquid crystal in the vicinity of the nematic-smectic A transition

The resistance to shear flow is investigated theoretically for polar liquid crystals, such as 4- n -octyl- 4'- and 4- n -octyloxy-4'-cyanobiphenyls. It is established that the lowest resistance to shear flow at temperatures in the vicinity of the nematic-smectic A phase transition point T NA is observed when the nematic director is ori- ented perpendicular to both the flow velocity vector and the flow velocity gradient. The three Miesowicz shear viscosity coefficients η i ( i = 1-3) at temperatures close to the phase transition temperature (tens of millikelvins from T NA ) and far from this transition are calculated in the framework of the Ericksen-Leslie theory. The decrease in the viscosity coefficients in the order η 2 > η 1 > η 3 is explained by the fact that fluctuations of the local smectic order in the nematic phase lead to a singular behavior of the viscosity coefficient η 2 , whereas the other two viscosity coefficients η 1 and η 3 are not affected by order parameter fluctuations. © 2004 MAIK "Nauka/Interperiodica".

Sun Glint Contamination in ATSR-2 Data: Comparison of Observations and Values Calculated from the Measured 1.6-μm Reflectivities

Abstract The effect of radiation from the sun reflected at the sea surface on the 11- and 12-μm brightness temperatures measured by the Along-Track Scanning Radiometer ATSR-2 has been investigated. An attempt was made to determine its magnitude by comparing nadir-view and forward-view brightness temperature differences in glint and nonglint regions, and the results are compared with theoretical predictions computed by using the 1.6-μm reflectivity data. Atmospheric absorption and the polarization sensitivity of the instrument have been fully taken into account. The results show that temperature increases of a few tens of millikelvins are possible even over the open ocean, and that they correlate well with the measured 1.6-μm reflectivity values. A scheme for correcting the sun glint contamination is proposed.

Apparent tricritical behavior at a nearly second-order nematic-isotropic phase transition of a cyclic liquid crystalline trimer.

The cyclic liquid crystalline trimer TPB-(c)9(3) was investigated by optical retardation and Fréedericksz techniques within a few tens of millikelvins of the superheating limit of the nearly second-order nematic-isotropic phase transition. Both the optical retardation and the Fréedericksz bend threshold voltage are in good agreement with tricritical behavior for the transition.

Variable Property Piston Effect

The use of the van der Waals equation of state for numerical simulation of the piston effect results in underpredicting the magnitude of the pressure wave by 38% while overpredicting the acoustic heating by 13% compared to using a real gas equation of state from the National Institute of Standards and Technology. When evaluating the piston effect at conditions typical of cryogenic storage systems, the pressure response of the fluid was observed to be tens of kilopascals. This pressure response was six orders of magnitude larger than had been reported in previous research. The extent of the acoustic heating resulted in temperature increases in the bulk fluid that was measured in tens of milliKelvins. Previous researchers reported temperature increases in microKelvins, four orders of magnitude smaller than observed in this research effort.

Proximity effect thermometer for local electron temperature measurements on mesoscopic samples

Using the strong temperature-dependent resistance of a normal metal wire in proximity to a superconductor, we have been able to measure the local temperature of electrons heated by flowing a direct-current (dc) in a metallic wire to within a few tens of millikelvin at low temperatures. By placing two such thermometers at different parts of a sample, we have been able to measure the temperature difference induced by a dc flowing in the samples. This technique may provide a flexible means of making quantitative thermal and thermoelectric measurements on mesoscopic metallic samples.

An investigation of the stability of thermistors

In order to better characterize thermistors, a group of 405 bead-in-glass and disc thermistors were aged in constant temperature baths. Samples of 135 thermistors were aged in each of three constant temperature baths held at 0, 30, and 60 °C. Each sample was composed of 65 bead-in-glass and 70 disc thermistors which represented a total of six manufacturers and six resistance values. The thermistors were maintained at temperature for 550 to 770 days and their resistances and the bath temperatures were periodically monitored. Analysis of the data revealed systematic differences between bead-in-glass and disc thermistors upon ageing and indicated a dependence of ageing behavior on bath temperature and resistance value. Drift rates within groups of thermistors from each manufacturer were fairly uniform. Large initial changes in the drift rate for the disc thermistors at 30 and 60 °C (and to a much lesser extent in the bead-in-glass thermistors) require that thermistors for use at an accuracy level of a few tens of millikelvins be aged prior to use.

λ-Transition between normal and superfluid 4He in the high–speed rotating frame

THE rotating helium cryostat (1-m diameter, 3,000 r.p.m.) at Southampton provides a novel way of studying the behaviour of liquid helium. The centrifugal acceleration fields (up to 5,000g at the periphery) enable pressure differences up to 20 bar to be generated in radial ducts containing liquid helium between the axis and the periphery of the rotor. We have recently rotated the cryostat at temperatures down to 1.8 K, well below the λ-transition to superfluid helium. The λ-transition temperature is suppressed by increasing pressure so that the rotor becomes a unique tool for the study of the phase transition boundary between normal helium He(I) and superfluid helium He(II). Here we report observations of a step-like temperature difference of several tens of millikelvin across the boundary. The temperature jump can be explained in terms of the positive value of the volume coefficient of expansion for He(I) over a finite temperature interval above the λ-line, and the presence of a non-convecting intermediate state of finite thickness separating the two phases.